Multifunction aircraft sensor probes are known, such as the multifunction aircraft probe assemblies disclosed in the above-cited Baltins et al '526 patent. In this regard, the probe assemblies of the Baltins et al '526 patent are generally embodied in a rotatable airstream direction probe which is additionally provided with a dynamic pressure sensing port positioned substantially midway between a pair of pneumatic sensing ports which are symmetrically positioned with respect to the probe's stagnation line. A set of pneumatic output ports may thus be provided, each of which communicates with a respective one of the pneumatic sensing ports in the probe.
Thus, when the pneumatic pressures within the paired sensing ports are balanced, the pneumatic pressure at the output port(s) in communication with the sensing ports will be essentially at a pressure P.sub.1 which is a monotonic function of static (atmospheric) pressure over a wide range of airspeeds (e.g., from 0.1 Mach to supersonic speeds). The dynamic pressure sensing port, on the other hand, will be presented directly to the airstream when the pressures within the pneumatic sensing ports are balanced. As a result, a dynamic pressure output port which communicates with the dynamic pressure sensing port will exhibit a maximum airstream pressure P.sub.0 which is a monotonic function of pitot (ram) pressure over a wide range of airspeeds. These pressures P.sub.1 and P.sub.0 can thus be converted mathematically into actual pitot (ram) and static (atmospheric) pressures undiluted by any error dependent upon the aircraft's angle of attack and/or side slip. The probe can thus be employed to derive angle of attack and/or side slip flight data information, in addition to primary flight data, such as airspeed, altitude and/or vertical speed.
The airstream temperature represents important information that may be used by on-board instrumentation. For example, actual airstream temperature can be employed to determine the true airspeed of the aircraft during flight (e.g., indicated airspeed compensated by airstream temperature and pressure conditions). Furthermore, airstream temperature is important to initiate activation either manually or automatically of the aircraft's on-board anti-icing equipment.
In-flight airstream temperature data have been determined conventionally using an airstream temperature probe remotely located at a fixed positioned relative to the airstream pressure sensing probe(s). This remote placement of the temperature probe can induce some slight, but meaningful, data errors. In this regard, conventional temperature probes include a resistive thermal device (RTD), a thermally protective shell, and an outer body. The typical RTD, usually made of platinum for temperature stability properties, varies in electrical resistance as a function of sensed temperature. The protective shell serves to protect the RTD from any debris/ice/moisture which may enter the outer body and to protect the RTD from sensing any temperature variation from the heated outer body. The function of the outer body is to duct enough air through the body to allow for dynamic temperature sensing while minimizing the impact of any debris entering from the airflow. To ensure proper airflow, the outer body is heated to prevent ice build-up and reduce moisture content of the air flow through the body.
Conventional aircraft air temperature probes, like pitot probes, are mounted in a fixed position with a large forward-facing opening to minimize error from misalignment with the air flow. However, since both devices measure stagnation (or total) properties of the air flow, measurements of air flows at large incoming angles relative to the forward-facing opening will have an uncorrectable error causing the indicated measurements to be less than stagnation (or total) measurements.
Thus, it would especially be desirable if aircraft temperature probes could be provided which are not susceptible to uncorrectable errors caused by relatively large angles of incoming air flow (which might occur at relatively large angles of attack). It is towards fulfilling such a need that the present invention is directed.
Broadly, the present invention is directed toward an aircraft air temperature probe which is capable of being maintained in substantial alignment with the airstream stagnation line (or line of highest airstream pressure impinging on the probe element's external surface).
In accordance with a particularly preferred embodiment of this invention, the airstream temperature sensor is provided collectively as an integral part of a multifunction aircraft probe assembly of the type disclosed in the Baltins et al '526 patent and/or the Menzies et al '072 application. In this regard, the airstream temperature probe is most preferably isolated physically from the probe assembly's airstream pressure sensing ports, but is capable of being aligned with such sensing ports with the airstream's stagnation line.
In one particularly preferred embodiment, the probe element of this invention is provided with at least one pressure sensing port and a temperature sensing port which are in fluid communication with a pressure sensing chamber and a temperature sensing chamber, respectively, and are each alignable as a unit with respect to the airstream stagnation line. A temperature sensor may thus be disposed in the temperature sensing chamber so as to sense the temperature of the in-flight air flow.
The temperature sensor is most preferably shielded thermally from the probe element. Specifically, the temperature sensor is most preferably coaxially surrounded by a generally cylindrical thermal shield structure having airflow inlet and outlet apertures. The thermal shield thereby prevents the temperature of the probe element (which may be heated by an integral electrical resistance heater during potential in-flight icing conditions) from affecting the airflow temperature data obtained by the temperature sensor.
These and other aspects and advantages of the present invention will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.